Method of treating permeable formations

ABSTRACT

A method is provided for grouting zones of permeable geologic formations to prevent the flow of fluid through the grouted zone. In this method the formation is penetrated by a borehole. A blasting agent is disposed in the borehole contiguous to the zone to be grouted. The blasting agent is detonated to provide fractures in the zone of the formation which extend radially away from the borehole. The fractures are grouted to prevent the flow of fluid through the grouted zone.

United States Patent Tregembo et al.

[ Sept. 12, 1972 [54] ,METHOD OF TREATING PERMEABLE FORMATIONS [72] Inventors: Rhoderio Tregembo, Grants, N.

Mex. 87020; Wayne R. Dolezal, Grants, N. Mex. 87020; Lowell D. Boughton, Tulsa, Okla. John D. Stewart, Littleton, Colo. 80120 [73] Assignee: The Dow Chemical Company, Mid-- land, Mich. and Kern-McGee Cor- 3 -.EEEMEPEEQEE 9911 99- [22] Filed: Feb. 24, 1970 [21] Appl. No.: 13,452

[52] US. Cl. ..61/36, 166/299, 175/72 [51] Int. Cl. ..E02d 3/12 [58] Field of Search "61/35, 36, 53, 54; 166/286, 166/299; 175/57, 72

[56] References Cited UNITED STATES PATENTS 1,009,159 11/1911 Lodwick ..6l/36R 1,106,606 8/1914 Wilhelmi ..6l/53.54 1,449,236 3/1923 Malone ..61/53.54

1,734,670 11/1929 Greene ..166/286X 2,313,109 3/1943 Wertz ..61/36 R 2,591,807 4/1952 Greene ..166/286 2,627,169 2/1953 Poulter ..61/35 3,026,096 3/1962 Love ..61/36 R X 3,190,373 6/ l 965 Weathersby ..166/286 3,191,678 6/1965 Hinson ..166/299 3,300,984 1/1967 Armentrout ..61/36 R X Primary ExaminerDavid J. Williarnowsky Assistant ExaminerPhilip C. Kannan Attorney-Griswold and Burdick, Bruce M. Kanuch and William R. Norris [5 7] ABSTRACT A method is provided for grouting zones of permeable geologic formations to prevent the flow of fluid through the grouted zone. In this method the formation is penetrated by a borehole. A blasting agent is disposed in the borehole contiguous to the zone to begrouted. The blasting agent is detonated to provide fractures in the zone of the formation which extend radially away from the borehole. The fractures are grouted to prevent the flow of fluid through the grouted zone.

16 Claims, 11 Drawing Figures PATENTED 3.690.106

sum 2 OF 4 l \I 11 J V 9 INVENTORS. LOWELL D. BOUGHTO/V JOHN D. STEWART RHODER/C TREGEMBO AVA/ER. DOLEZGL BY Ad U flTTOR/VEY PATENTEBSEP 12 I972 SHEET 3 OF 4 METHOD OF TREATING PERMEABLE FORMATIONS BACKGROUND OF THE INVENTION It is often desirous to prevent the flow of fluids through certain zones of geologic formations, e.g., aquifers. For example, fluid producing formations encountered when drilling petroleum wells, when creating shafts, tunnels and other types of underground passageways, such as, when connecting underground passageways with the surface of the earth can cause serious problems. Also, foundations upon which large buildings or dams are being prepared usually must be impermeable to the flow of water and the like. In the past various methods have been employed in an attempt to prevent such flow from or through certain zones of such formations. For example, grouting material has been forced into natural occurring fissures and fractures in such formations to partially prevent the flow of fluids. Likewise, such formations have been hydraulically fractured to produce additional fractures which are then grouted. However, these means are not always successful because such formations do not al ways contain natural occuring fractures which can be grouted to prevent the flow of fluids. Likewise, a sufficient amount of hydraulic pressure cannot always be exerted on such formations to provide a sufficient number of additional fractures for effectively shutting off fluid flow. Also, since the drilling is performed in relatively dry formations (after treatment thereof by the present invention) air drilling can be employed instead of circulating drilling muds. This can constitute substantial savings in the operation.

SUMMARY OF THE INVENTION In the present method a permeable formation is penetrated by at least one treatment borehole. A sufficient amount of a blasting agent is disposed in the borehole contiguous to the zone of the formation desired to be grouted. The explosive is detonated to provide a multiplicity of fractures extending radially away from said borehole. Rubble, if any, may then be removed from the borehole and the fractures grouted to reduce the permeability of the formation in the fractured and grouted zone. The permeable formations may be producing undesirable fluids, e.g., an aquifer, which it may be desired to reduce, and/or it may be a formation through which the flow of fluids is to be restricted, e.g., supporting formations upon which structures are to be built.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. l-4 illustrate one embodiment of the present invention where a fluid bearing formation is treated by the method of the present invention to prevent the flow of fluid into a large diameter shaft.

FIG. 5 illustrates the configuration of the drilling pattern for the method described in Example 2.

FIGS. 6 and 7 illustrate still another embodiment of the present invention wherein a large underground area is treated by the method of the present invention to prevent the flow of fluids through formations forming support for a structure, e.g., a dam.

FIGS. 8 and 9 illustrate another embodiment of the instant invention employing treatment holes drilled in an angled spiral configuration.

FIGS. 10 and 11 illustrate two embodiments of the present invention as applied to the treatment of a fluid bearing formation through which a substantially horizontal tunnel is to be prepared. In FIG. 10 the treatment boreholes are drilled down from the surface of the earth and the formation is fractured and grouted by the method of the present invention to provide a grouted zone through which the tunnel can be prepared. In FIG. 11 the treatment bore(s) (more than one if necessary) is drilled ahead of tunnel and the fluid bearing formation treated in a like manner. The number of treatment boreholes shown is merely illustrative, the exact number employed is dependent on the size of the formation to be treated, the type of explosive employed and other like conditions.

DETAILED DESCRIPTION OF THE INVENTION In the practice of the present invention the permeability of a permeable geologic formation penetrated by at least one treatment borehole is reduced in the following manner. A predetermined amount of a blasting agent is disposed within the treatment borehole(s) contiguous to the permeable formation desired to be treated. The blasting agent is detonated producing multiple fractures in said formation extending radially away from the treatment borehole. In many instances intersecting, cross-connecting fractures are I also produced. Rubble, if any, is then preferably removed from the borehole and the fractures, and, if desired, the so produced cavity is grouted to prevent the flow of fluid through the fractured zone.

The present invention can be employed to prepare openings, e.g., shafts, boreholes, tunnels, etc., which have a relatively large diameter, e.g., a few feet or more. Because of the large diameter it may be impractical to attempt to fracture permeable formations penetrated by such openings with a blasting agent. In the present method, therefore, at least one smaller treatment borehole is first drilled and the permeable I formation treated, i.e., fractured and grouted, employing the treatment borehole as the base of operation.

With reference to FIGS. 1-4 one embodiment of the present invention is practiced as follows. It is desired to sink an opening, e.g., shaft, borehole, etc., having a final diameter 10, for example to connect with an underground passageway 17. At least one smaller treatment borehole l 1 is first provided, e.g., drilled, approximately concentric and along the vertical axis of the desired hole 10. When the smaller treatment borehole l1 penetrates a fluid producing formation 12, FIG. 2,

, e.g., an aquifer, drilling is temporarily stopped. A

predetermined amount of a blasting agent 13 is disposed in the treatment borehole 11 contiguous, i.e., adjacent, to the fluid producing formation 12. As will be more fully discussed hereinafter a sufficient amount of a particular blasting agent is provided so that upon the detonation thereof fractures will be produced in the fluid bearing formation 12 extending a known distance from and around the treatment borehole 1 1. In this embodiment the fractures should extend a distance greater than the diameter of the final hole 10. The blasting agent 13 is then detonated to produce the fractures 14, FIG. 3, extending radially away from the treatment borehole 11 and a distance greater than the diameter of the final hole 10, FIG. 3. The fractures are then grouted with a suitable material 15 in a manner known in the art, i.e., the material is pumped into the treatment borehole and fractures under pressure. The blasting and grouting operations are repeated a sufficient number of times to substantially arrest the flow of fluid from the formation 12 and into the treatment borehole. When the fluid bearing formation 12 has been treated as described above a grout curtain occupying the zone 16 is produced which substantially arrests the flow of fluid into treatment borehole l1 and the final hole 10. The smaller treatment borehole is then continued to the desired depth, e.g., to connect with the passageway 17. If other fluid bearing formations are penetrated in sinking the treatment borehole they can be treated in a like manner. The final hole is then prepared in a manner known in the art. For example, as shown in FIG. 4, the smaller treatment borehole 11 is upreamed or raise drilled (with an upreaming apparatus 18). Since the grouted zone 16 extends outwardly from the treatment borehole 11, a distance greater than the diameter of the final opening 10, fluid is substantially prevented from flowing through the treated formation and into the opening 10.

When an extremely large borehole is to be prepared the procedure shown in FIG. 5 can be employed. In this embodiment, several smaller treatment boreholes 11 are prepared in a pattern such that when the fluid hearing formation is fractured and grouted in the manner described herein the fractures and grout will overlap to again form a grouted zone (defined in FIG. 5 by the series of overlapping circles 19), which is greater than the final desired opening.

Fluid bearing formations over which dams or other structures are to be built can be stabilized by employing the method of the present invention. Fluid, e.g., water, can be prevented from flowing through such supporting formations in the following manner. For example, FIGS. 6 and 7 illustrate a method of fracturing and grouting a foundation, consisting of natural rock, of a dam 20. The rock has sufficient permeability that water impounded by the dam would flow through the formation. A line A of treatment boreholes 11 is drilled across the complete extent of the rock foundation which is to be covered by the impounded water. If desired a second line B of treatment boreholes 11 is also drilled across the foundation at the wider part of the dam where water might enter the foundation from the fill material making up the dam. A blasting agent is loaded into the holes at a depth whereby the radially created fractures will intersect the surface of the earth, (as shown in FIG. 7) as well as providing overlapping and intersecting fractures with the adjoining holes and lines of holes, to provide a zone defined by overlapping circles 19. The blasting agent is detonated and the resulting radial and cross connecting fractures (and preferably the treatment boreholes) are grouted to form an impermeable zone of sufficient length and width to prevent water leaking through the rock foundation of the dam. A sufficient number of rows of treatment boreholes are provided to effectively treat the formation.

FIGS. 8 and 9 illustrate even another embodiment of the present method. In this embodiment a grouted zone is provided which encircles the opening 10. The specific method for drilling the treatment boreholes 11 is described in The Canadian Mining and Metallurgical Bulletin, Vol. 56, No. 6 l0, pages. 94-103, February (1963). In that description a method is taught for treating water producing formations encountered when sinking a large diameter mine shaft 10 (2I feet in diameter) employed to mine potash in Canada. In the method therein defined, treatment boreholes 11, (therein described as probes) are drilled at an angle to the vertical axis of the desired shaft, in a spin pattern, illustrated herein in FIGS. 8 and 9, to detect the presence of water bearing formations 12. In the method described in the Journal when a water producing formation 12 was penetrated it was grouted under pressure. However, it was taught that great difficulties were encountered in effecting complete arresting of the flow of water because of the high grouting pressures needed to displace the grouting material into the formation. In the practice of the present invention the water-producing formation is first fractured by disposing a blasting agent in the treatment boreholes 11, contiguous to the formation 12 and detonated to generate fractures 14 extending radially from and around the treatment boreholes 1 l. The formation is then easily grouted with a suitable material to provide a grouted zone 16 which in this instance encircles the final shaft 10.

As illustrated in FIG. 9, the treatment boreholes l1 can be provided at a number of different levels 20 and 21 while preparing the shaft 10; the treatment boreholes 11 are simply made from the floor of the shaft 10 at any desired level. In this manner the treatment boreholes l 1 do not have to be extended over the entire length of the desired shaft 10.

The present invention is applicable to horizontal, vertical and angled bores, wells, tunnels, shafts and the like.

When employing multiple treatment boreholes to create a fractured zone the number of boreholes required and the distance they should be spaced apart to assure that overlapping and intersecting fractures are produced must be calculated. These parameters are dependent upon the composition and amount of the blasting agent employed and upon the type and depth of the formation to be fractured. These parameters can be calculated by formulas well known in the art. For example, in the present invention any blasting agent can be employed which has sufficient power and brisance that upon detonation thereof the permeable formation is fractured over a desired zone. In boreholes located deep in the earths formation, e.g., oil wells, elevated pressures are commonly incurred. Blasting agents which are detonable under these existing pressures must be employed. Self-explosive type blasting agents, e.g., nitrogen containing organic explosives, for example, nitroglycerine and the like, can be employed in the present invention. Also, inorganic oxidizing salt based blasting agents well known in the art can be used. Exemplary of a blasting agent which can be employed where elevated pressures are encountered is described in U.S. Pat. No. 3,456,589. The teachings of this patent are specifically incorporated herein by reference. Exemplary of other blasting agents which can also be employed are taught in U.S. Pat. No. 3,10l,288, said teachings being incorporated herein by reference. The power and brisance of blasting agents can be determined by methods well known in the art. Also, the

length of fractures which can be produced in certain earthen formations upon detonation of a given amount of a blasting agent can be calculated by formulas well known in the art.

One such formula is readily applied to an inorganic oxidizing salt based blasting agent containing the following constituents, as per cent by weight: forrnamide about 10 percent, water about 10 percent, sodium nitrate about 9 percent, ammonium nitrate about 36 percent, particulate aluminum about 27 percent, gums, thickeners, dispersants and inhibitors about 2 percent, and hollow glass spheres about 6 percent, said blasting agent being sold under the trademark Stratablast A. The length of fractures which can be produced upon detonation of a given amount of this composition within a rock formation of given hardness is N 2W wherein N is the length of fracture in feet; V is the volume of the explosive in the borehole in cubic inches and 2 is a power constant based upon data obtained from blasting tests employing explosives of varying strengths and densities in rock formations of varying hardness. Thus 2 for Stratablast A has been determined to be about 2 when fracturing hard rock and about 1.2 in soft rock; 1.6 is taken as an average. The blasting agent (Stratablast A) has a density of about 1.2 gm/cc or about 75 pounds per cubic foot. It has also been estimated that the amount of rubble, i.e., volume of rock which is fragmented enough to be removed from the formation after the blasting agent is detonated is about 10 to 20 times the volume of explosive used. The following Table sets forth a number of calculated radial fracture distances employing the formula set forth hereinbefore for the Stratablast A blasting agent.

TABLE I Calculated Radial Fracture Hole Length of Pounds of Distance in Feet Diameter Charge stratablastA E=l.2 E=L6 E=2.0

max. 8" 4'0" 105 16 21 26 9" 4' 6" 150 I8 24 30 I" 0" 205 22 30 37 I2" 6' 0" 350 24 32 4O 14" 7'0" 565 28 37 47 I4" 8' 0" 840 32 43 53 I8" 9' 0" 1200 36 48 60 2O" 0" 1650 40 53 67 24" 4' 0" 950 33 44 56 8' 0" 1900 42 56 70 12 0 2850 48 64 80 28" 4' 0" I275 37 49 61 8' 0" 2550 47 62 78 Other blasting agents may be employed in this invention in the same manner as the Stratablast A blasting agent taking into account the characteristics of the individual agent. A common blasting agent which is operable in the process is an ammonium nitrate-fuel oil mixture, commonly known as ANFO containing about 94 percent by weight of ammonium nitrate and about 6 percent fuel oil. The E values for ANFO are 1.0 in soft rock and 1.2 in hard rock, i.e., granite. Other operable blasting agents, by way of example, are gelatin dynamite, available under the trademark Gelex No. 2, having a value of about 1.2 for rock of average hardness; TNT with 2 values of 1.3 in hard rocks such as granite and basalt and 1.1 in elastic rocks such as shales, and a percent aluminizedpercent TNT balance ammonium nitrate composition having a 2 value of about 1.4 for rocks of average hardness.

After the blasting agent has been loaded into the treatment borehole it is preferred to tamp it. Suitable tamping materials are known in the art and include for example, pea gravel, crushed rock, angular sand and the like.

Grouting materials which can be employed in the practice of the present invention are those materials known in the art for arresting the flow of fluids in permeable formations. A cementitious material is employed when a substantially permanent grouted zone is desired. Examples of such cementitious materials are hydraulic cements known in the well drilling art, examples of which are described in the Encyclopedia of Chemical Technology, 2nd Edition, 1964, vol. 4, pages 64-97 and Building Construction Handbook, 2nd Edition, 1958, Section 2, pages 2-1 through 2-28. Also, cementitious gels of organic polymers such as disclosed in US. Pat. No. 3,306,870 and patent application Ser. No. 486,530, filed Sept. 10, 1965 can be employed in the present invention. The teachings of these patents and application are incorporated herein by reference. Other materials include, for example, inorganic gels, e.g., sodium silicate gels and the like.

EXAMPLE 1 A uranium mine-ventilation shaft was prepared connecting the surface of the ground with a drift. The final diameter of the shaft was 60 inches. The shaft was made by drilling. First an 8%-inch diameter pilot hole was started from the surface of the earth by conventional methods using a rotary drilling rig. At the depth of 381 feet a water producing formation had been penetrated; 240 pounds of Stratablast A blasting agent were loaded into the hole from 381 feet back up to about 374 feet, being in the water producing formation. The blasting agent was armed with a booster and a detonation timing device and then the hole stemmed with a layer of clay over which was placed pea gravel. After the blasting agent had been detonated the rubble from the explosion was cleaned out to a depth of 363 feet. At this point the circulating drilling fluid used with the rotary rig no longer returned to the surface, but leaked off into the rock formation. This indicated good communication had been established into the formation by the blasting operation. The blasted area was then grouted with a Portland cement slurry using 1,000 sacks of cement. This slurry was forced into the radial and interconnecting fractures resulting from the detonation of the blasting agent. When the cement had set it was found that there was no communication with the formation; all the drilling fluid circulated with no leak off. The pilot hole was drilled to a depth of 383 feet; it was noted again from the circulation of the drilling fluid that communication with the formation was re-established. The blasted area was again grouted in three stages with slurries of sacks each with a 5 minute interval between the stages. After the cement had set and drilling of the pilot hole was reinitiated there was no loss of drilling fluid, showing that an impermeable curtain of grout had been formed. Drilling was continued to a depth of 4 l 8 feet and 250 pounds of Stratablast A blasting agent was loaded into the hole and detonated to fracture another water producing formation encountered at this point. The fractured formation was then grouted with sacks of Portland cement. Testing showed the formation was plugged or curtained off. The pilot hole was drilled to a depth of about 453 feet when a third water producing strata was encountered. This formation was explosively fractured using 260 pounds of Stratablast A blasting agent. Good communication was established with the formation and the formation was grouted with a slurry of 500 sacks of Portland cement.

After the cement had set the hold was drilled out to 453 feet whereupon communication with the formation was re-established. The section was grouted with an additional slurry of 625 sacks of Portland cement. After the cement had set, testing showed no communication and drilling of the hole was continued to a final depth of 750 feet without further blasting and grouting. Drilling to this depth brought the 8 /-inch pilot hole into the drift and the hole was enlarged to 60inch diameter by raise drilling. As this was done no water was produced from the three water-producing intervals of formation, the intervals having been explosively fractured and grouted off by the method of the present invention for a radial distance greater than the 60-inch diameter of the enlarged shaft. Other shafts located in the immediate area of the ventilation shaft and penetrating the same water producing formations were completed prior to the work exemplified by Example 1 and without employing the method of the present invention. The water production in these shafts is very troublesome, being in the range of 200-300 gallons per minute.

EXAMPLE 2 The method of the present method was employed to prepare a production shaft extruding from the surface of the earth into a uranium mine. The treatment borehole pattern and the grouted area are shown in FIG. 5. Several aquifers existed between the surface and the mine. To prepare the shaft the following procedure was employed. Three treatment boreholes, 11, were employed. A first treatment borehole (8% in diameter) was drilled and the water producing formations treated several times by fracturing the formation with a blasting agent consisting of the Stratablast A composition defined hereinbefore. Then the fractured zone was grouted with cement (a modified Portland cement sold under the trademark Sloflo).

The blasting and grouting procedure was repeated eleven times during the drilling of the treatment borehole. The levels at which the formations were blasted and grouted, and the amount of explosive and cement employed are set forth in the following Table II.

Testing for water production following each blasting and grouting operation showed substantially no water being produced in the first treatment borehole. In a similar fashion, a second treatment borehole (later employed for electrical power cables) and a third treatment borehole (later employed for a pump column) were drilled, blasted, and grouted. These latter two boreholes were located triangularly about 30 feet each from the first treatment borehole and about 30 feet apart and were drilled to approximately the same total depth. Consequently, they encountered the samev aquifers. The aquifers penetrated by each borehole were blasted and grouted. No measurable water production was present in either of these two boreholes. The overlapping circles 19 shown in FIG. 5 illustrate the zones fractured and grouted by this work. Tables III and IV show the extent of the blasting and grouting work in the final two treatment holes.

TABLE III Depth, Stratablast A, Portland Cement,

Feet Pounds Sacks TABLE IV Depth, Stratablast A, Portland Cement,

Feet Pounds Sacks After the three treatment boreholes were completed, a 2-inch diameter evaluation hole located approximately equidistant from the three and within the projected grout curtain of each, was drilled to the same depth as the three treatment boreholes. The evaluation hole was tested for production of water and found to be dry for the entire length, being effectively curtained by the blasting and grouting of the three surrounding holes, i.e., the zone created by overlapping circles 19. The 2- inch evaluation hole was enlarged to a 16% foot diameter mine shaft to a final depth of about 780 feet; again little or no water was produced from the various aquifers treated by the method of the present invention.

What is claimed is:

1. A method of penetrating a permeable formation at a predetermined location with an opening of a predetermined size which comprises:

a. penetrating said formation with at least one treatment borehole which has a diameter substantially smaller than the size of the opening;

b. disposing an explosive within said treatment borehole contiguous to the formation, said explosive having sufficient power and brisance and being provided in an amount sufficient to produce multiple fractures extending radially away from the treatment borehole in said formation upon detonation thereof to produce a fractured zone which is larger than the size of the opening;

0. detonating the explosive to produce said fractured zone;

d. grouting the fractures a sufficient distance to provide a grouted zone larger than the size of said opening; and I e. penetrating the grouted zone with said opening.

2. The method as defined in claim 1 wherein the rubble formed in the formation upon the detonation of the explosive is substantially completely removed therefrom prior to grouting fractured zone.

3. The method as defined in claim 1 wherein the opening is a shaft connecting the surface of the ground with an underground passageway.

4. The method as defined in claim 1 wherein the opening is non-vertical.

5. The method as defined in claim 1 wherein said permeable formation is an aquifer.

6. The method as defined in claim 1 wherein the explosive is tamped prior to being detonated.

7. The method as defined in claim 1 wherein the opening is substantially vertical.

8. A method of creating an opening having a predetermined size in a subterranean permeable formation which comprises:

a. penetrating the formation with a plurality of treatment boreholes, each borehole having a diameter substantially smaller than the size of said opening;

b. disposing an explosive charge in each borehole contiguous to said formation, said explosive having sufficient power and brisance and being provided in a sufficient amount such that upon detonation of each explosive charge fractures are produced in the formation around each borehole which extend a sufficient distance to intersect and overlap with fractures produced around at least one other treatment borehole, said treatment boreholes being provided in a pattern such that a continuous fractured zone is produced upon detonation of the explosive charges, the size of said zone being larger than the size of said opening;

c. detonating the explosive charges to provide said continuous fractured zone in said formation;

d. grouting the fractured zone; and

e. creating the opening within the grouted zone.

9. The method as defined in claim 8 wherein rubble produced upon the detonation of each explosive charge is substantially completely removed from the treatment boreholes prior to grouting the fractured zone.

10. The method as defined in claim 8 wherein said explosive charges are tamped prior to being detonated.

11. The method as defined in claim 8 wherein said grouting material is cementitious.

12. The method as defined in claim 8 wherein said opening is a shaft extending from the surface of the earth.

13. The method as defined in claim 8 wherein the permeable formation is an aquifer.

14. The method as defined in claim 8 wherein the opening is a shaft to be connected with an underground passageway and each permeable formation located between the surface of the earth and the underground passageway through which the shaft extends is treated as defined by steps (a) through (d) of claim 8, prior to preparing the opening through each permeable formation.

15. The method as defined in claim 14 wherein the permeable formation is an aquifer.

16. The method as defined in claim 8 wherein the opening is non-vertical.

OFFICE RECTIQ Dated September 12, 1972 Patent No. 106

Inventor-(s) Rhoderio Tregembo, W. R. Dolesal, L. D. Boughton, J. D. Stewart It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

FEE-

Column 4, line 44, change "formulas" to -formulae--.

Column 5, item 6, column 1 of Table I, delete the second appearance of "14'' and insert --l6.

Column 5, line 62, after "a" and before "value" insert 3 Signed and sealed this 2 'rth day of April 1973.

(Si-AL) Attest:

EDWARD 15., FLETCHERJ'R. ROBERT GOTTSCHALK ttesting Officer Commissioner of Patents 

1. A method of penetrating a permeable formation at a predetermined location with an opening of a predetermined size which comprises: a. penetrating said formation with at least one treatment borehole which has a diameter substantially smaller than the size of the opening; b. disposing an explosive within said treatment borehole contiguous to the formation, said explosive having sufficient power and brisance and being provided in an amount sufficient to produce multiple fractures extending radially away from the treatment borehole in said formation upon detonation thereof to produce a fractured zone which is larger than the size of the opening; c. detonating the explosive to produce said fractured zone; d. grouting the fractures a sufficient distance to provide a grouted zone larger than the size of said opening; and e. penetrating the grouted zone with said opening.
 2. The method as defined in claim 1 wherein the rubble formed in the formation upon the detonation of the explosive is substantially completely removed therefrom prior to grouting fractured zone.
 3. The method as defined in claim 1 wherein the opening is a shaft connecting the surface of the ground with an underground passageway.
 4. The method as defined in claim 1 wherein the opening is non-vertical.
 5. The method as defined in claim 1 wherein said permeable formation is an aquifer.
 6. The method as defined in claim 1 wherein the explosive is tamped prior to being detonated.
 7. The method as defined in claim 1 wherein the opening is substantially vertical.
 8. A method of creating an opening having a predetermined size in a subterranean permeable formation which comprises: a. penetrating the formation with a plurality of treatment boreholes, each borehole having a diamEter substantially smaller than the size of said opening; b. disposing an explosive charge in each borehole contiguous to said formation, said explosive having sufficient power and brisance and being provided in a sufficient amount such that upon detonation of each explosive charge fractures are produced in the formation around each borehole which extend a sufficient distance to intersect and overlap with fractures produced around at least one other treatment borehole, said treatment boreholes being provided in a pattern such that a continuous fractured zone is produced upon detonation of the explosive charges, the size of said zone being larger than the size of said opening; c. detonating the explosive charges to provide said continuous fractured zone in said formation; d. grouting the fractured zone; and e. creating the opening within the grouted zone.
 9. The method as defined in claim 8 wherein rubble produced upon the detonation of each explosive charge is substantially completely removed from the treatment boreholes prior to grouting the fractured zone.
 10. The method as defined in claim 8 wherein said explosive charges are tamped prior to being detonated.
 11. The method as defined in claim 8 wherein said grouting material is cementitious.
 12. The method as defined in claim 8 wherein said opening is a shaft extending from the surface of the earth.
 13. The method as defined in claim 8 wherein the permeable formation is an aquifer.
 14. The method as defined in claim 8 wherein the opening is a shaft to be connected with an underground passageway and each permeable formation located between the surface of the earth and the underground passageway through which the shaft extends is treated as defined by steps (a) through (d) of claim 8, prior to preparing the opening through each permeable formation.
 15. The method as defined in claim 14 wherein the permeable formation is an aquifer.
 16. The method as defined in claim 8 wherein the opening is non-vertical. 